unsure where you get your trace mix from but both APF and TNC chelated trace elements contain Iron (Fe) and are infact from the same wholesaler
😉
http://www.aquariumplantfood.co.uk/fertilisers/dry-chemicals/chelated-trace.html
https://www.thenutrientcompany.com/product/tnc-trace-at/
It's me who has really hijacked
@a1Matt thread asking about using an all in one in a high tech situation as if it was possible I didn't see the need for using 2 separate mixes.
I'm sure someone will correct a few things here as I don't fully understand it all but the whole thing about the iron is it reacting with Potassium phosphate and that's the whole reason why EI is dosed separately in a nutshell.
By lowering the PH of the solution to below PH6 the iron should not react which is where the ascorbic acid comes in, the potassium sorbate is there as a preventative against mould etc.
The iron that comes in the trace mixes above is EDTA and different types of chelated iron exist that are stronger such as DTPA which I'm told is the one to go for.